Process for preparing di(aminophenyl)-methanes

ABSTRACT

Di(aminophenyl)methane having a high proportion of the o,p&#39;&#39;isomer (10 to 60 percent) and a substantial proportion of the o, o&#39;&#39;-isomer (5 to 25 percent) is obtained by reacting at least 3.5 moles of aniline with 1 mole of formaldehyde, separating the water of condensation from the resulting mixture of aniline and anilino-acetal, heating the anhydrous mixture to 125* C. to 205* C. and adding a proton source (aniline hydrochloride preferred). The mixture of di(aminophenyl)-methane isomers can be separated from the mixture of polyamines so obtained and phosgenated to give a mixture of the corresponding isomeric di(isocyanatophenyl)methanes which mixture is a storage stable liquid. Alternatively the mixture of polyamines can be phosgenated, without separation of the di(aminophenyl)-methane, to give the corresponding mixture of polymethylene polyphenyl polyisocyanates. The latter mixture gives polyurethane foams of much lighter color than those obtained using comparable mixtures produced by prior art procedures.

United States Patent Recchia et a1.

[54] PROCESS FOR PREPARING DI(AMINOPHENYL)-METHANES [72] Inventors:Frank P. Recchia, New Haven; Henri Ulrich, North Branford, both of Conn.

[73] Assignee: The Upjohn Company, Kalamazoo, Mich.

[22] Filed: Aug. 6, 1968 [21] Appl. No.: 750,454

[52] U.S. Cl. ..260/570 D, 260/2.5 AT, 260/453 AM, 260/566 R, 260/5705 P[51] Int. Cl ..C07c 85/08 [58] Field of Search ..260/570, 453 R, 570 D[56] References Cited UNITED STATES PATENTS 2,015,039 9/1935 Pevere..260/570 2,683,730 7/1954 Seeger et al. .....260/453 2,818,433 12/1957Erickson ..260/570 2,950,263 8/1960 Abbotson et al. ..260/2.5 3,260,7517/1966 Powers et al ..260/570 3,277,173 10/1966 Powers et al ..260/5703,297,759 l/l967 Curtiss et al ..260/570 3,362,979 l/1968 Bentley.260/570 X 3,476,806 1 H1969 Wolf ..260/570 3,499,009 3/1970 Odinsk etal ..260/570 OTHER PUBLICATIONS Allied Chemical, Avilive," page 35(1965).

Primary Examiner-Robert V. Hines Attorney-Eugene O. Rctter and Denis A.Firth 57 ABSTRACT Di(aminophenyl)methane having a high proportion of theo,p'-isomer 10 to 60 percent) and a substantial proportion of theo,o'-isomer (5 to 25 percent) is obtained by reacting at least 3.5 molesof aniline with 1 mole of formaldehyde, separating the water ofcondensation from the resulting mixture of aniline and anilino-acetal,heating the anhydrous mixture to 125 C. to 205 C. and adding a protonsource (aniline hydrochloride preferred). The mixture ofdi(aminophenyl)- methane isomers can be separated from the mixture ofpolyamines so obtained and phosgenated to give a mixture of thecorresponding isomeric di(isocyanatophenyl)methanes which mixture is astorage stable liquid. Alternatively the mixture of polyamines can bephosgenated, without separation of the di(aminophenyl)-methane, to givethe corresponding mixture of polymethylene polyphenyl polyisocyanates.The latter mixture gives polyurethane foams of much lighter color thanthose obtained using comparable mixtures produced by prior artprocedures.

10 Claims, No Drawings PROCESS FOR PREPARING DI(AMINOPHENYL)- METHANESBACKGROUND OF THE INVENTION 1. Field ofthelnvention This inventionrelates to di(aminophenyl)methanes having substantial o,p'-isomer ando,o'-isomer content, to a-process for the preparation thereof, and tothe corresponding isocyanates produced from said di(aminophenyl)methanesand from mixtures of methylene bridged polyphenyl polyamines containingsaid di(aminophenyl)methanes.

2. Description of the'Prior Art The preparationofdi(aminophenyl)methane, and mixtures of methylene-bridged polyphenylpolyamines containing said diamine, by acidcondensation of aniline andformaldehyde, is well-known in the art; see, for example, U.S. Pat. No.2,638,730. This reaction has become of considerable commercialimportance. The diamine itself, and mixtures of polymethylene polyaminescontaining .the diamine as the principal ingredient (which mixtures arethe product of the anilineformaldehyde condensation), are usefulas suchin the polymer art as curing agents for epoxy resins and for elastomericpolyurethanes. Said diamine and the mixed polyamines containing it arealso useful as intermediates in the preparation, by phosgenation, of thecorresponding diand polyisocyanates.

The diisocyanate so obtained is widely used in the preparation ofelastomeric polyurethanes while the polymethylene polyphenylpolyisocyanates obtained in the above manner, are widely used in thepreparation of polyurethane foams.

The di(aminophenyl)methanes prepared by acid condensation of aniline andformaldehyde in accordance with procedures commonly used hitherto arefound to consist mainly (90 percent by weight or greater) of thep,p'-isomer and to contain only minor amounts (less than percent byweight) of the corresponding o,p'-isomer. Said products contain nosubstantial amounts of the other theoretically possible isomer, namelythe o,o'-isomer. It is found that the di(isocyanato-phenyl)methanesprepared from such diamines are solids of low melting point (circa 40C.) and, accordingly, have to be melted and maintained molten in orderto be dispensed through conventional mixing machines employed in thecommercial preparation of polyurethanes. A number of ways of convertingsuch di(isocyanato-phenyl)methanes to storage stable liquids have beenadopted; see, for example, U.S. Pat. No. 3,384,653.

Recently there have been described methods for preparingdi(aminophenyl)methanes which contain substantially higher proportionsof o,p'-isomer to p,p'-isomer and it has been found that such mixturesgive rise, upon phosgenation, to corresponding mixtures ofdi(isocyanato-phenyl)methanes which are liquid at ambient temperaturesand hence possess marked advantages overthe low melting soliddi(isocyanato-phenyl)methane hitherto available. Illustratively, U.S.Pat. No. 3,3 62,979 describes the preparation of a liquid form ofdi(isocyanatophenyl)methane containing from 20 to 95 percent by weightof the 2,4'-is0mer, the remainder of said mixture being 4,4 -isomer.Said diisocyanate is obtained by phosgenation of the correspondingisomeric mixture of di(aminophenyl)methanes which latter mixture isobtained by condensation of aniline and formaldehyde in the presence ofan acidic siliceous catalyst. In the condensation formaldehyde is addedto a mixture of aniline and catalyst at a temperature of 100 C. to 300C. and water is continuously removed from the reaction mixture.

In U.S. Pat. No. 3,277,173 there is described a method of obtainingdi(aminophenyl)methane containing a substantial proportion of the2,4'-isomer by carrying out the Lewis acid catalyzed reaction of anilineand formaldehyde in the presence of a carefully controlled amount ofwater (including the water of condensation).

Belgian Pat. No. 648,787 described the preparation of di-(aminophenyl)methane containing substantial proportions of o,o-isomerand o,p'-isomer in addition to p,p'-isomer by employing high finalreaction temperatures in the hydrochloric acid catalyzed condensation ofaniline and formaldehyde.

We have now found that di(aminophenyl)methanes in which the proportionsof o,o'-isomer and o,p'-isomer are substantial, can beprepared using anovel procedure which is possessed of marked economic advantages SUMMARYOF THE INVENTION This invention comprises a process for the preparationof di(aminophenyl)methane in which the proportion of o,p'- isomer and0,0 '-isomer is substantial said process comprising:

mixing aniline and formaldehyde in proportions such that the aniline ispresent in an amount corresponding to at least about 3.5 moles per moleof formaldehyde;

removing the water of condensation liberated in the anilineformaldehydereaction product;

heating the resulting anhydrous product to a temperature of about 125 C.to about 205 C.;.and

adding thereto a catalytic amount of a proton source.

The invention also comprises the di(aminophenyl )methanes so producedeither in purefied form or as part of a mixture of methylene-bridgedpolyphenyl polyamines obtained in accordance with the process of theinvention. The invention also comprises thedi(isocyanato-phenyl)methanes and polymethylene polyphenylpolyisocyanates obtained by phosgenation of said diamine and polyaminemixtures.

DETAILED DESCRIPTION OF THE INVENTION In the first step of the processof the invention aniline and formaldehyde are brought together in theabsence of acid or any other catalyst hitherto employed in the art. Thereaction is conducted substantially in accordance with the proceduredescribed by Cohn, Zeitschrift fur Ang. Chem. XIV, 1901, 31 1. Thus theaniline and formaldehyde are brought together in any convenient manner,advantageously with stirring. The aniline can be added to theformaldehyde or vice versa. However, it is preferred to add theformaldehyde to the aniline. The formaldehyde is preferably in the formof an aqueous solution, i.e., in the form of the 37 percent aqueoussolution which is the form most readily available commercially. However,the formaldehyde can also be used in one of its polymerized forms i.e.as paraformaldehyde or trioxymethylene, if desired. The temperature atwhich the reactants are brought together is not critical. For the sakeof convenience the reactants are generally brought together at ambienttemperatures (circa 20 to 25 C.) but higher or lower temperatures can beemployed if desired. The reaction is exothermic but can be readilycontrolled either by appropriately adjusting the rate of addition ofreactant or by applying external cooling, if necessary. Although, asindicated previously, the reaction temperature in this stage of thereaction is not critical it is preferable that the temperature of thereaction mixture does not rise above about C. during this phase of thereaction. Since water is eliminated in this reaction and the reactiontemperature cannot rise above the boiling point of the aqueous mixture,there is an automatic upper limit imposed on the temperature at whichthe reaction in this first stage occurs.

The reaction taking place between the aniline and formaldehyde in thisphase of the reaction is rather complex but the simplest reactionoccurring can be represented by the following equation:

(.lellsNllz (MIC-11 CalIr-N -Cllz H20 i.e., equimolar proportions inaniline and formaldehyde condense with the elimination of a molecule ofwater and the formation of the compound (I) which is variously known asanhydroformaldehydeaniline" (see Cohn, supra) and as the.

anilinoacetal of formaldehyde.

As will be appreciated by one skilled in the art, the anilino acetal (I)can undergo further condensation. Illustratively the following reactioninvolving a second molecule of aniline can occur:

c n xzcng (3611mm CGH5NH-CII2-NHC1I5 The latter material can undergoreaction with a further molecule of aniline and of formaldehyde inaccordance with the following equation:

The product so obtained can undergo further similar condensation withformaldehyde and aniline to give more complex molecules. All of thereaction products so obtained can be described generically asanilinoacetals of formaldehyde and will be so designated hereinafter.

Since, as indicated above, an excess of at least 3.5 moles, per mole offormaldehyde, of aniline is always employed in the process of theinvention the reaction product obtained in the first step of saidprocess is a mixture of (a) the above mixture of the anilinoacetals offormaldehyde and (b) excess aniline.

It has been found that the use of smaller proportions of aniline toformaldehyde than the minimum set forth above leads to the formation ofsignificant amounts of undesirable by-products in the process of theinvention. Chief of said byproducts are the N-methyl substitutedderivatives of the desired end products.

While the lower limit of the molar proportion of aniline to formaldehydeemployed in the first stage of the reaction is dictated by the desire toavoid the production of unrequired byproducts, the upper limit is notcritical and is dictated largely by economic considerations.

Generally speaking the proportion of aniline to formaldehyde employed inthe first step of the process of the invention determines the proportionof di(aminophenyl)methane to higher polymethylene polyphenyl amines inthe end-product. Thus, within limits, the higher the molar proportion ofaniline to formaldehyde in the first step of the process of theinvention the higher the proportion of di(aminophenyl)methane in theeventual reaction product. However, no significant increase inproportion of di(aminophenyl)methane in the reaction product is observedwhen the molar proportion of aniline to formaldehyde is increased aboveabout 8:1. Accordingly, the latter represents the practical upper limitof said proportions although, obviously, higher proportions can beemployed without derogating from the overall results achieved in theprocess of the invention.

The reaction between the aniline and formaldehyde in the first step ofthe process of the invention occurs very rapidly even at ambienttemperatures. The progress of the reaction can be followed byconventional analytical techniques e.g., by following the disappearanceof formaldehyde from the reaction mixture, or by following the amount ofwater liberated in the condensation, etc. When the reaction is observedto have proceeded to completion the next stage of the process of theinvention is initiated.

1n the second stage of the process of the invention, the water ofcondensation eliminated in the first stage of the process is separatedfrom the reaction mixture. Since the water separates as a distinct layerin the reaction mixture, the separation can be carried out simply bysiphoning off or decanting the organic layer from the aqueous layer.However, in order to render the reaction mixture anhydrous the lasttraces of water have to be removed from the organic layer bydistillation or like techniques. Accordingly, it is generally mostconvenient to carry out the separation of the organic and aqueous layersby simple distillation, long tube evaporation, and like methods, ifdesired, under reduced pressure.

The anhydrous mixture of anilinoacetals so obtained is then submitted tothe third stage of the process of the invention. In this stage theanhydrous mixture is heated to a temperature which is within the rangeof about to 205 C. and preferably within the range of about to C.Advantageously, the time taken to heat the reaction mixture to theselected temperature is short i.e., is less than about one hour.Preferably the time taken to accomplish the heating of the reactionmixture is less than 15 minutes. Similarly, after the reaction mixturehas been brought to the desired temperature, the time taken to completethe third stage of the process of the invention is short. Prolongedheating of the reaction product at this stage can result in undesirableby-products due to other than the desired rearrangement of some of theanilinoacetals in said reaction mixture. Accordingly, the total timetaken in heating the reaction mixture to the desired temperature and inholding the reaction mixture at said temperature is preferably less thanone hour and most preferably is less than 30 minutes.

When the anhydrous reaction mixture from the second stage of the processof the invention has been brought to a temperature within the aboverange, a catalytic amount of a proton source is added to the reactionmixture. By catalytic amount is meant an amount less than 1 molarequivalent of catalyst per mole of reactant in the reaction mixturebeing treated. Advantageously, the amount of proton source added is lessthan 0.2 molar equivalents per mole of reactant and preferably is fromabout 0.01 molar equivalents to about 0.03 molar equivalents, per moleof reactant.

The term proton source is used in its conventionally accepted sense asindicating a material which will generate a proton. Thus, said term isinclusive of inorganic and organic acids which dissociate, at least inpart, with the formation of a proton. Said term is also inclusive ofaddition salts of the aforesaid acids with ammonia and primary,secondary or tertiary amines, which salts dissociate, at the reactiontemperature employed in the third stage of the process of the invention,and release the free acid as a proton source. Illustrative of saidinorganic and organic acid proton sources are inorganic acids such ashydrochloric acid, hydrobromic acid, hydriodic acid, hydrofluoric acid,sulfuric acid, phosphoric acid, silicic acid, fluosilicic acid,phosphomolybdic acid, and the like; and organic acids particularlyhydrocarbon carboxylic acids from one to 12 carbon atoms, inclusive,such as alkanoic acids, for example, formic, acetic, butyric, caproic,caprylic, and lauric acids, alkane dicarboxylic acids, for example,oxalic, malonic, succinic, glutaric, adipic, and sebacic acids, alkenoicacids, for example, acrylic, crotonic, and the like, aromatic carboxylicacids, for example, benzoic, toluic, phthalic, isophthalic,terephthalic, a-naphthoic, B-naphthoic, and the like, and araliphaticcarboxylic acids such as phenylacetic, phenylpropionic,a-naphthaleneacetic acid, phenylvaleric acid, and the like.

The above inorganic and organic acids can be used in the free acid asthe proton source in the third stage of the process of the invention orcan be employed in the form of addition salts with ammonia or primary,secondary, and tertiary alkylamines such as methylamine, dimethylamine,trimethylamine, ethylamine, triethylamine, methylethylamine,methyldiethylamine, butylamine, isobutylamine, hexylamine,N-methylhexylamine, octylamine, N-ethyloctylamine, N,N-diethyloctylamine, and the like; primary, secondary, and tertiaryalkenylamines such as allylamine, crotonylamine, methallylamine,2-hexenylamine, 3-octenylamine, diallylamine, N- methylallylamine,N-methyl-N-ethyl-allylamine, and the like; primary, secondary andtertiary cycloalkylamines such as cyclobutylamine, cyclopentylamine,cyclohexylamine, cyclooctylamine, N-methylcyclohexylamine,N,N-dimethylcyclohexylamine, and the like; primary, secondary, andtertiary cycloalkenylamines such as cyclopentenylamines,cyclohexenylamine, cycloheptenylamine, cyclooctenylamine,N-ethylcyclohexenylamine, N,N-diethylcyclohexenylamine, and the like;primary, secondary, and tertiary aralkylamines such as benzylamine,benzhydrylamine, Z-phenethylamine, 3- phenylpropylamine,N-methylbenzylamine, N-methyl-N- ethylbenzylamine,N,N-diisopropylbenzylamine, and the like;

primary, secondary, and tertiary aromatic amines such as aniline, oc,m-, and p-toluidine, m-xylidine, p-xylidine, mphenylenediamine,p-phenylenediamine, a-naphthylamine, B- naphthylamine, N-methylaniline,N-methyl-N- isopropylaniline, N,N-dimethylaniline, N,N-diethylaniline,N- methyl-o-toluidine, and the like; and heterocyclic secondary andtertiary amines such as pyridine, pyrrolidine, N-methylpyrrolidine,2-methyl-pyrrolidine, piperidine, N-ethylpiperdine, piperazine,N-methylpiperazine, N,N-dimethylpiperazine, morpholine,Z-methyl-morpholine, N-methylmorpholine, N-ethylmorpholine, quinoline,and the like.

In additionto the various free acids and acid addition salts set forthabove another source of protons are the complexes of acrylonitrile withhydrogen halides such as the hydrogen chloride complexes; see, forexample, U.S. Pat. No. 2,411,064. Such complexes release hydrogen halideat the reaction temperatures called for in the third step of the processof the invention.

While any of the acids described and exemplified above can be employed,either in the form of the free acid or in the form of an addition salt,in the third step of the process of the invention, we prefer to use ahydrogen halide either in the form of the free acid or in the form of anaromatic amine salt. The most preferred proton source for use in theprocess of the invention is a hydrogen halide addition salt of anilineof which aniline hydrochloride is the ultimate preferred choice. The useof aniline hydrochloride has the advantage not only of liberatinghydrogen halide but of employing the same aromatic amine as that whichis already present in the reaction mixture. Hence the use of this saltas the proton source avoids the introduction of extraneous moleculeswhich cannot enter into the main reaction which is occuring in theprocess of the invention.

In carrying out the third step of the process of the invention, theproton source can be introduced into the anhydrous reaction mixture(after heating to the desired temperature within the range hereinbeforegiven) in any convenient manner and either in one batch or in portionsover a period of time. Advantageously, the addition is made while thereaction mixture is being subjected to vigorous agitation.

This step of the process of the invention is readily adapted tooperation on a continuous basis. Thus, in one such continuous operationthe reaction product from the second stage is passed through a heatexchanger to bring it to the desired reaction temperature and thenthrough a reaction zone in which it is maintained under conditions ofturbulent flow while addition of the proton source is made. Theresulting mixture is then removed from the reaction zone and worked upas described below.

The time taken for the reaction to proceed to completion, after theaddition of the proton source has been accomplished in the third stageof the process of the invention, varies according to the reactiontemperature employed. Generally speaking, the time 'in question is veryshort and varies from less than 1 minute to about minutes. The progressand completion of the reaction can be followed using conventionalanalytical procedures such as infrared spectroscopy, 11] travioletspectroscopy, and the like. When the reaction in the third step of theprocess of the invention is found to have reached completion, thereaction product is cooled, or allowed to cool, to room temperature andthen treated to isolate the desired product using proceduresconventionally employed in the art for the working up of polyaminemixtures derived from the aniline formaldehyde condensation. Forexample, the reaction mixture is neutralized, if desired, by theaddition of sodium hydroxide, potassium hydroxide and like bases. It isto be noted that, when the amount of proton source employed in the thirdstep of the process of the invention is very small, it is generally notnecessary to employ a neutralization step in the working up of thereaction product. This represents an additional advantage in the novelprocess of the invention.

After neutralization, if such is necessary, the reaction product isdistilled to remove excess aniline which may be present. The residue soobtained is a mixture of methylene bridged polyphenyl polyaminescontaining di(aminophenyl)- methane as the principal product. Thismixture can be used as such for a variety of purposes including thepreparation, by phosgenation, of polymethylene polyphenylpolyisocyanates which can be used to obtain polyurethane foams havingmarkedly better color properties than heretofore. Alternatively, thepolyamines can be treated, as by fractional distillation,chromatography, and the like, to recover the diamine therefrom. Thelatter is also useful in the preparation of the correspondingdi(isocyanato-phenyl)methane which, in contrast to the diisocyanatecontaining high proportions of 4,4- isomer, has the advantage of being astable liquid product at all normal working temperatures (15 to 25 C.).Indeed, we have obtained in this manner mixtures of isomericdiisocyanates which have a freezing point as low as 40 C. and which haveshown no separation of solids on standing at ambient temperatures (20 to25 C.) for many months.

As previously mentioned the di(aminophenyl)methane obtained inaccordance with the process of the invention, whether in the form of theisolated diamine or of the mixture of methylene-bridged polyphenylpolyamines, contains a substantial proportion of the o,p'-isomer and asomewhat smaller but significant proportion of the o,o'-isomer. Indeed,under certain conditions it is possible to obtain mixtures in which theo,p'-isomer is the predominant component of the mixture.

The proportions of the p,p'-isomer, o,p'-isomer and o,o'- isomer in thedi(aminophenyl)methane obtained by the process of the invention can varywithin the range of about 15 percent to about percent by weight ofp,p'-isomer, about 10 percent to about 60 percent by weight ofo,p-isomer, and about 5 percent to about 25 percent by weight ofo,o'-isomer. The isomer proportion obtained in any given case is afunction of the temperature at which the reaction is conducted in thethird step of the process of the invention. In general the proportion ofo,p'-isomer and of o,o'-isomer increases, and the proportion ofp,p'-isomer correspondingly decreases, as the reaction temperatureincreases within the range set forth above. The requisite reactiontemperature to obtain any given isomer proportion can be determinedreadily by a simple process of trial and error.

The mixture of methylene-bridged polyphenyl polyamines containingdi(aminophenyl)methane which is produced in accordance with theinvention differs from corresponding mixtures obtained using procedureshitherto known in the art not only by reason of the differences inproportions of the various isomeric di(aminophenyl)methanes but also byreason of significant differences in proportions of the trimers,tetramers, and higher polymeric components. That this is so is readilyapparent from a comparison of the gel permeation chromatographic spectraof representative polyamine mixtures prepared in accordance with theinvention and in accordance with the prior art. Not only is theproportion of total trimers to total tetramers, total tetramers to totalpentamers, etc. different but the distribution of the various possibleindividual trimers, tetramers etc. in the products is markedlydifferent.

It is believed that this difierence in the proportions of the variouspolymeric materials in the polyamine mixtures produced in accordancewith the invention is one factor which may be responsible for theunexpected and advantageous difference in properties between thepolymethylene polyphenyl polyisocyanates produced by phsogenation of thepolyamine mixtures obtained in accordance with the present invention andthe corresponding polyisocyanates produced from prior art polyaminemixtures.

The following examples describe the manner and process of making andusing the invention and set forth the best mode contemplated by theinventors of carrying out the invention but are not to be construed aslimiting.

EXAMPLE 1 A total of 8.14 g. (0.1 mole) of 36.9 percent w/w formaldehydesolution was added slowly with stirring over a period of 45 minutes to74.5 g. (0.8 mole) of aniline. The temperature of the reaction mixturerose from an initial value of 25 C. to a maximum of 32 C. When theaddition was complete the mixture was stirred for 2 hours atapproximately 25 C. At the end of this period the mixture was heated to190 C. over a period of minutes with removal of water by distillationusing a side arm take-off head. To the resulting hot mixture was added,all at once, 3.11 g. (0.024 mole) of aniline hydrochloride. Thetemperature of the mixture increased rapidly to 192 C. and wasmaintained in the range of 190 to 192 C. for 5 minutes after theaddition of the aniline hydrochloride. The mixture so obtained was thencooled immediately to 25 C. using an ice water bath and made alkaline bythe addition of ml of 50 percent aqueous sodium hydroxide solution. Theproduct was steam distilled to remove excess aniline and the organiclayer in the undistilled residue was extracted with methylene chloride.The methylene chloride extract was washed with water until the washingswere neutral to litmus. The washed extract was dried over anhydrousmagnesium sulfate, filtered, and the filtrate was evaporated to dryness.There was thus obtained 17 g. (85.8 percent theoretical yield based onformaldehyde) of a mixture of methylene-bridged polyphenyl polyamineswhich was found by gel permeation chromatography (G.P.C.) and gas liquidphase chromatography (G.L.P.C.) (using internal standards based onsynthetic mixtures of pure materials) to contain 78.0 percent by weightof di(aminophenyl)methane of which 39.4 percent by weight was4,4-isomer, 43.2 percent by weight was 2,4'-isomer, and 17.4 percent byweight was 2,2'-isomer.

Using essentially the same conditions as those described above andvarying only the proportions of aniline and aniline hydrochloride twofurther runs were carried out. The proportions of reactants, reactionconditions and yield and composition of end-product in these runs issummarized in Table 1 below. The molar proportion given for anilineincludes the aniline added as aniline hydrochloride in the last stage ofthe process. The yield and proportions of isomeric diamines weremeasured using G.L.P.C. as described above.

obtained, as the undistilled residue, 16.5 g. of a mixture ofmethylene-bridged polyamines which was found by G.L.P.C. to contain 78.9percent by weight of methylene dianilines of which 56.0 percent byweight was the 4,4-isomer, 35.2 percent by weight was 2,4-isomer and 8.8percent by weight was 2,2'-isomer.

EXAMPLE 3 The procedure described in Example 2 was repeated exactly withthe sole exception that the reaction product, obtained after removal ofwater from the aniline-formaldehyde condensate, was heated to 170 C.before addition of the aniline hydrochloride. The mixture of methylenebridged polyamines so obtained weighed 16.6 g. and was found by G.L.P.C.to contain 78.5 percent by weight of methylene dianilines of which 48.3percent by weight was the 4,4'-isomer, 39.5 percent by weight was the2,4'-isomer and 12.2 percent by weight was the 2,2'-isomer.

EXAMPLE 4 A total of 66 pounds of 37 percent aqueous formaldehyde wasadded slowly, with agitation, over a period of one hour to 450 pounds ofaniline. The temperature rose from an initial value of21 C. to a finalvalue of 38 C. at the end of the addition. When the latter was completethe mixture was heated with stirring at 40 C. for 2 hours. The waterpresent in the reaction mixture was allowed to separate and was decantedoff the organic layer. The latter was then heated under reduced pressureto remove the last traces of water. The residual dry aminal mixture wascharged to a continuous back mix reactor and heated to 180 C. With thereactor contents at this temperature gaseous hydrogen chloride waspumped into the reactor at a rate of 0.4 g. per minute. At the end of 10minutes fresh dry aminal mixture (prepared as described above) was addedto the reactor continuously at a rate of 50 ml per minute and reactionproduct was withdrawn from the reactor at the same rate. Throughout thisperiod the flow of gaseous hydrogen chloride was maintained at 0.4 g.per minute. Subsequently the addition rate of fresh aminal was raised to80 ml per minute and the gaseous hydrogen chloride rate to 0.9 g. perminute. Finally the fresh aminal addition rate was raised to TABLE IMolar proportions of reactants lsomer distribution,

--- Reaction Reaction Diapercent Formaltemp. time mines, Aniline dehydeHCl 0.) (min.) percent 2,2 2,4 4,4

EXAMPLE 2 160 ml per minute and the gaseous hydrogen chloride rate to Atotal of 8.2 g. (0.1 mole) of 36.6 percent aqueous formaldehyde solutionwas added slowing with stirring to 74.5 g. (0.8 mole) of aniline at sucha rate as to maintain the temperature of the mixture at about 40 C.After the addition was complete, the resulting mixture was agitated fora further 2 hours at ambient temperatures (approximately 20 C.). Themixture so obtained was distilled at atmospheric pressure until nofurther water was collected in the distillate. The undistilled residuewas heated rapidly to 150 C. with stirring and 3.1 l g. (0.024 mole) ofaniline hydrochloride was added in one batch. The temperature of thereaction rose rapidly to 155 C. and then subsided. The reaction mixturewas maintained at 150 C. with stirring for minutes and was then cooledrapidly to 20 C. and made alkaline by the addition of 3.8 g. (0.048mole) of percent aqueous sodium hydroxide solution. A small quantity ofwater was added to the reaction during this stage. The excess anilinewas removed from the neutralized reaction mixture by steam distillation.The undistilled residue was extracted with three successive portions(each 100 ml.) of benzene. The benzene extracts were combined, washedwith water, dried over anhydrous magnesium sulfate and filtered. Thefiltrate was distilled to remove benzene. There was thus 1.6 g. perminute. Samples of reaction product removed at each of these threelevels of aminal addition were analyzed for MDA-isomer content byG.L.P.C. and found to be as follows:

lsomer Content A second run was carried out using the above procedurebut increasing the amount of aniline employed from 450 pounds to 562pounds and using a fresh aminal addition rate of 50 ml per minute and agaseous hydrogen chloride addition rate of 0.4 g. per minute. Themixture of polyamines so obtained was found by G.L.P.C. to contain 63.3percent methylene dianilines of which 12.3 percent by weight was2,2'-isomer, 40.8 percent by weight was 2,4-isomer and 46.9 percent byweight was 4,4'-isomer.

A solution of 1,655 g. of the latter mixture of polyamines in 3,000 mlof anhYdrous monochlorobenzene was added slowly a a A n4 with stirringand cooling at about over a period of 1.5 hours to a solution of 2,500g. of phosgene in 7,000 ml of monochlorobenzene. When the addition wascomplete the mixture was heated gradually to a temperature of 120 C. andmaintained thereat (120 to 128 C.) for 6 hours while a stream ofphosgene was passed through the reaction mixture. At the end of thistime the excess phosgene was purged from the reaction mixture using astream of nitrogen. The bulk of the monochlorobenzene was then removedusing a long tube evaporator under reduced pressure at about 60 C. Theresidual monochlorobenzene was distilled away under vacuum at a maximumtemperature of 150 C. There was thus obtained a mixture of polymethylenepolyphenyl isocyanates having a methylenebis(phenyl isocyanate) contentof 63 percent. This mixture was subjected to distillation at reducedpressure. A forecut of 1 1.4 g. was removed followed by a total of 333.6g. of methylenebis(phenyl isocyanate) distilling at 155 C. at 0.5 mm ofmercury. This diisocyanate was found to have an isocyanate equivalent of125.2 and, by G.L.P.C., to have an isomer content as follows: 21.9percent 2,2-isomer; 49.0 percent 2,4'-isomer; and 29.1 percent4,4'-isomer. The undistilled polymethylene polyphenyl polyisocyanaterecovered from the above distillation was found by G.L.P.C to contain32.3 percent methylenebis(phenyl isocyanate) of which 9.8 percent byweight was 2,2'-isomer, 40.1 percent was 2,4'-isomer and 50.1 percent byweight was 4,4'-isomer.

EXAMPLE 5 Using the phosgenation procedure described in the laterportion of Example 4 above, the polyamine mixture containing 73 percentby weight of di(aminophenyl)methane, prepared as described in Example 1above, was converted to the corresponding mixture of polymethylenepolyphenyl polyisocyanates. The latter contained 73 percent by weight ofmethylenebis(phenyl isocyanates) of which 41 percent by weight was4,4'-isomer, 41 percent by weight was 2,4'-isomer and 18 percent byweight was 2,2'-isomer.

Similarly, using the phosgenation procedure described in Example 4above, the various polyamine mixtures prepared as described in Examples1 to 3 above were converted to the corresponding polymethylenepolyphenyl polyisocyanates having a content of methylenebis(phenylisocyanate) and a ratio of isomers in the latter corresponding to thesame content and isomer ratios of diamines in the starting polyaminemixture.

We claim:

1. In a process for the preparation of di(aminophenyl)- methane in whichthe proportion of p,p'-isomer is from about 15 to about percent byweight, the proportion of o,p'- isomer is from about 10 to about 60percent by weight and the proportion of o,o-isomer is from about 5 toabout 25 percent by weight the steps of:

mixing aniline and formaldehyde in proportions such that the aniline ispresent in an amount corresponding to at least about 3.5 moles per moleof formaldehyde;

removing the water of condensation liberated in the anilineformaldehydereaction product; heating the resulting anhydrous product to atemperature of about C. to about 205 C.;

and adding thereto under anhydrous conditions a catalytic amount of aproton source selected from the class consisting of hydrogenhalides,alkanoic acids from one to 12 carbon atoms, inclusive, and thesalts of said hydrogen halides and said alkanoic acids with aromaticamines.

2. The process of claim 1 wherein the proton source is hydrogenchloride.

3. The process of claim 1 wherein the proton source is an aromatic aminehydrochloride.

4. The'process of claim 3 wherein the proton source is anilinehydrochloride.

5. The process of claim 1 wherein the anhydrous aniline-formaldehydecondensation product is heated at to C. during addition of the protonsource.

6. In a process for the preparation of di(aminophenyl)- methane whereinthe p,p'-isomer content is from about 15 to about 85 percent by weightthe o,p-isomer content is from about 10 to about 60 percent by weight,and the o,o'-isomer content is from about 5 to about 25 percent byweight, based on total di(aminophenyl)-methane, the steps of: heating ananhydrous mixture of aniline and anilinoacetals, obtained bycondensation of formaldehyde with excess aniline, to a temperature ofabout 125 C. to about 205 C. and adding thereto under anhydrousconditions a catalytic amount of a roton source selected from the classconsisting of hydrogen alides and the salts thereof with aromaticamines.

7. The process of claim 6 wherein the proton source is hydrogenchloride.

8. The process of claim 6 wherein the proton source is an aromatic aminehydrochloride.

9. The process of claim 6 wherein the proton source is anilinehydrochloride.

10. The process of claim 6 where the reaction temperature is within therange of 185 to 190 C. during the addition of the proton source.

2. The process of claim 1 wherein the proton source is hydrogenchloride.
 3. The process of claim 1 wherein the proton source is anaromatic amine hydrochloride.
 4. The process of claim 3 wherein theproton source is aniline hydrochloride.
 5. The process of claim 1wherein the anhydrous aniline-formaldehyde condensation product isheated at 185* to 190* C. during addition of the proton source.
 6. In aprocess for the preparation of di(aminophenyl)-methane wherein thep,p''-isomer content is from about 15 to about 85 percent by weight theo,p''-isomer content is from about 10 to about 60 percent by weight, andthe o,o''-isomer content is from about 5 to about 25 percent by weight,based on total di(aminophenyl)-methane, the steps of: heating ananhydrous mixture of aniline and anilinoacetals, obtained bycondensation of formaldehyde with excess aniline, to a temperature ofabout 125* C. to about 205* C. and adding thereto under anhydrousconditions a catalytic amount of a proton source selected from the classconsisting of hydrogen halides and the salts thereof with aromaticamines.
 7. The process of claim 6 wherein the proton source is hydrogenchloride.
 8. The process of claim 6 wherein the proton source is anaromatic amine hydrochloride.
 9. The process of claim 6 wherein theproton source is aniline hydrochloride.
 10. The process of claim 6 wherethe reaction temperature is within the range of 185* to 190* C. duringthe addition of the proton source.